Methods of manufacturing arrays of thin magnetic elements and arrays produced by the methods

ABSTRACT

This specification describes a method of manufacturing an array of data storage elements from thin sheet material, each element having at least one perforation for data entry and read-out conductors, in which a sheet of the magnetic material with the perforations for the elements is annealed whilst a magnetic field is applied across the sheet thereby to form lines of easy magnetization around the perforations and material is then removed from the sheet to form the separate storage elements. Examples of suitable magnetic materials include binary and ternary alloys of iron, nickel and cobalt.

O United States Patent [151 3,662,357 Enoch 1 May 9, 1972 54] METHODS OF MANUFACTURING 3,123,808 3/1964 Ward ..340/174 ARRAYS OF THIN MAGNETIC 3,125,472 3/1964 Yamamoto et al. 148/ 108 ELEMENTS AND ARRAYS PRODUCED 3,183,567 5/1965 Riseman et a1. ....29/604 BY 3,493,944 2/1970 KOlk, Jr. ..29/604 X [72] Inventor: Reginald David Enoch, Pinner, England FOREIGN PATENTS OR APPLICATIONS 73 Assignee; The p offi London England 221,803 5/1959 Australia ..148/108 [22] Filed: 1970 Primary Examiner-L. Dewayne Rutledge 2 APPL 23 71 Assistant Examiner-G K. White Attorney-Hall & Houghton [30] Foreign Application Priority Data 57 1 ABSTRACT v Apl. 9, 1969 Great Britain ..l8,|63/69 This Specification describes a method of manufacturing an array of data storage elements from thin sheet material, each [52] }J.S.(il. ..340/174 TF,29/604, 148/108 element having at least one Perforation for data entry and 2; 'T'i: G1 read-out conductors, in which a sheet of the magnetic material 1 le o are with the perforations for the elements is annealed whilst a magnetic field is applied across the sheet thereby to form lines of easy magnetization around the perforations and material is [56] References Cited then removed from the sheet to form the separate storage ele- UNITED STATES PATENTS ments. Examples of suitable magnetic materials include binary 3 077 583 2/1963 R 340/174 and ternary alloys of iron, nickel and cobalt.

usse 3,089,222 5/1963 Eggenberger 9 Claims, 4 Drawing Figures PATENTEDMM 9:972 3,662,357

sum 1 0F 2 v REG/1w! 10 D, EA/aai/ INVENTOR I BY M 7% 4@\ ATTORNEY PATENTEUMAY 9 I972 3.662.357

sum 2 or 2 fiEd/IMLD 04 INVENTOR BY m fpd m ATTORNEY METHODS OF MANUFACTURING ARRAYS OF THIN MAGNETIC ELEMENTS AND ARRAYS PRODUCED BY THE METHODS This invention relates to the manufacture of arrays of thin magnetic data storage elements.

Magnetic storage elements are used .in random-access memories for computers and, in one form, the memory comprises an array of small elements of toroidal form whose magnetic condition is switched from one state of magnetic remanence to the other state by suitable current-carrying conductors.

For an element to be suitable for use in a memory, the following properties are required:

1. the material should have a rectangular hysteresis loop;

2. the coercivity of the material should preferably be less than Oe;

3. the switching time of the material under coincident current conditions should preferably be less than lOO sec.

It is an object of the invention to provide an improved method for the manufacture of an array of thin magnetic data storage elements from a ferro-magnetic material to which uniaxial anisotropic magnetic properties can be imparted.

According to one aspect of the invention there is provided a method for the manufacture of an array of thin magnetic data storage elements of thin anisotropic magnetic material, each element having at least one perforation around which runs a line of easy magnetization, comprising the steps of:

i. forming a thin sheet of thin magnetic material capable of having uniaxial anisotropic magnetic properties imparted to it, the sheet having a plurality of perforations,

ii. applying a magnetic field across the sheet whilst annealing the material to form lines of easy magnetization along the lines of force of the magnetic field,

iii. and then removing material from selected areas of the sheet whilst supported on an insulating non-magnetic substrate to produce a plurality of discrete elements on the substrate each having at least one perforation.

According to another aspect of the invention there is provided a data store including an array of elements manufactured by a method according to the preceding paragraph and for the elements through perforations therein conductor means for performing data entry and readout functions.

In order that the invention may be fully understood and readily carried into effect an embodiment will now be described. This embodiment is a data-store for a digital computer and a method for itsmanufacture. The data store comprises an array of thin ring-shaped anisotropic magnetic elements. The directions of easy magnetization of the elements are lines running around the central perforations of the discs.

The array may comprise a very large number of elements although only a few elements are illustrated in the drawings of which:.

FIG. 1 shows part of a sheet of magnetic material being prepared in accordance with an example of the invention;

FIG. 2 shows a detailed part of FIG. 1;

FIG. 3 shows part of an array of magnetic elements prepared in accordance with this example of the invention; and

FIG. 4 shows one of the elements of FIG. 3.

In FIG. 1 is shown part of a sheet 1 of magnetic material perforated by holes 2. The sheet may be of any thin material to which uniaxial anisotropic magnetic properties may be imparted by magnetic annealing. Suitable alloys for forming the thin sheet are those falling within the shaded areas in the ternary alloy diagram for nickel, cobalt and iron forming FIG. 2 on page 293 of Magnetic Properties of Metals and Alloys published in 1959 by the American Society for Metals. Alloys having a stronger magnetic annealing effect are preferable. Minor additions may be made to the alloys, as is well known, to increase the resistivity of the alloy and thereby reduce eddy current losses, but the proportion of such additions must be small enough to ensure that the Curie point does not fall below about 400C as otherwise the desired anisotropic properties will not be obtained within a conveniently short time. Other suitable materials will be known to those skilled in the art. The thickness of the sheet 1 is of the order of m and preferably less than this figure. The sheet 1 may be in either an annealed or cold-rolled state.

In one example, a sheet of 20uthickness was formed from an alloy comprising 37% nickel, 42% cobalt, 15% iron and 6% molybdenum on a substrate of SRPF sheet. After formation the sheet was annealed at 800C for 30 minutes and then cooled in a magnetic field of 2.5 Oe. Afier annealing the sheet was found to have a coercivity of 7.0 Oe.

The perforations 2 form the perforations in the elements around which lines of easy magnetization run. Thus the perforations 2 are arranged according to the desired layout of elements in the completed data store; in the example shown this is a square array.

The sheet 1 is placed in a furnace (not shown) and heated to a temperature in excess of its Curie temperature. As stated above the material of the sheet 1 is chosen to have the property that if it is cooled from a temperature above its Curie temperature to a temperature below that temperature in a sufficiently strong magnetic field, lines of easy magnetization will be formed along the lines of force of .the magnetic field through the material; this is one example of magnetic annealing.

A magnetic field is applied to the sheet 1 in the furnace so as to cross the whole of the sheet. FIG. 2 shows the lines of force 3 of the magnetic field about one of the perforations 2. The furnace is switched off and the sheet 1 is allowed to cool to room temperature in the presence of the field. As previously explained, lines of easy magnetization corresponding to the lines of force 3 of the magnetic field are formed in the sheet 1.

The sheet 1 is removed from the magnetic field and bonded to a substrate 4 (any suitable insulating non-magnetic material) over its entire face. Selected areas of the sheets 1 are then removed by, for example, etching following masking by conventional printed circuit techniques, to leave a plurality of discrete rings of magnetic material surrounding the perforations. The sheet 1 and substrate 4 will now have the appearance shown in FIG. 3. All of the sheet 1 has been removed except for rings 5 which form the data storage elements and are bonded to the substrate 4.

FIG. 4 shows one of the rings (or elements) 5 and the lines of easy magnetization 6 formed about the perforation 2.

Holes are made in the substrate 1 to coincide with the perforations 2 so that conductors may be threaded through the array to form a magnetic matrix data store.

In an alternative arrangement conductors for sense, digit and address functions may be formed by a printed circuit technique.

his not necessary for the elements to be circular, for example, they may alternatively be in the form of ellipses. In the case of elliptical (or other elongated) elements the magnetic field defining the easy direction of magnetization is preferably applied so as to be along the major axes of the ellipses.

The easy directions of magnetization may be formed by methods other than healing above the Curie temperature, for example, the sheet 1 may be isothermally annealed in the magnetic field at a temperature below the Curie temperature.

It will be appreciated that the invention enables a large number of elements to be fabricated from a single sheet of material with lines of easy magnetization running around each perforation in each element.

Arrays of elements other than the types mentioned can also be fabricated by a method according to the invention, for example, square elements with square holes or elements with several magnetic paths such as transfluxors.

We claim:

1. A method for the manufacture of an array of thin magnetic data storage elements of thin anisotropic magnetic material, each element having at least one perforation around which runs a line of easy magnetization, comprising the steps of:

i. forming a thin sheet of thin magnetic material capable of having uniaxial anisotropic magnetic properties imparted to it, the sheet having a plurality of perforations,

ii. applying a magnetic field across the sheet whilst annealing the material to form lines of easy magnetization along the lines of force of the magnetic field,

iii. and then removing material from selected areas of the sheet whilst supported on an insulating non-magnetic substrate to produce a plurality of discrete elements on the substrate each having at least one perforation.

2. A method according to claim 1, in which annealing the material includes cooling from a temperature above the Curie point of the material.

3. A method according to claim 1, in which the annealing of the material is carried out isothermally at a temperature below the Curie point of the material.

4. A method according to claim 1, in which the thin sheet of magnetic material is secured to an insulating non-magnetic substrate having perforations aligned with those in the magnetic material,

5. A method according to claim 1 including the formation of electrical conductor means passing through the perforations.

6. A data store including an array of elements manufactured by a method according to claim 5 with conductor means through the perforations in said elements for performing data entry and read out functions.

7. A store according to claim 6, in which the material of the thin sheet includes at least two of iron, cobalt and nickel.

8. A store according to claim 6 in which each element includes a respective perforation.

9. A store according to claim 8, in which the perforations are circular and the elements are in the form of annuli. 

2. A method according to claim 1, in which annealing the material includes cooling from a temperature above the Curie point of the material.
 3. A method according to claim 1, in which the annealing of the material is carried out isothermally at a temperature below the Curie point of the material.
 4. A method according to claim 1, in which the thin sheet of magnetic material is secured to an insulating non-magnetic substrate having perforations aligned with those in the magnetic material.
 5. A method according to claim 1 including the formation of electrical conductor means passing through the perforations.
 6. A data store including an array of elements manufactured by a method according to claim 5 with conductor means through the perforations in said elements for performing data entry and read out functions.
 7. A store according to claim 6, in which the material of the thin sheet includes at least two of iron, cobalt and nickel.
 8. A store according to claim 6 in which each element includes a respective perforation.
 9. A store according to claim 8, in which the perforations are circular and the elements are in the form of annuli. 